Display devices are used in a variety of applications. For example, thin film transistor liquid crystal displays (TFT-LCDs) are used in notebook computers, flat panel desktop monitors, LCD televisions, and Internet and communication devices, to name only a few.
Many display devices, such as TFT-LCD panels and organic light-emitting diode (OLED) panels, are made directly on flat glass sheets (glass substrates). To increase production rates and reduce costs, a typical panel manufacturing process simultaneously produces multiple panels on a single substrate or a sub-piece of a substrate. At various points in such processes, the substrate is divided into parts along cut lines (see, for example, the discussion of the “assemble and cut” and “cut and assemble” processes in Section V(B) below).
Such cutting changes the stress distribution within the glass, specifically, the in-plane stress distribution seen when the glass is vacuumed flat. Even more particularly, the cutting relieves stresses at the cut line such that the cut edge is rendered traction free. Such stress relief in general results in changes in the vacuumed-flat shape of the glass sub-pieces, a phenomenon referred to by display manufacturers as “distortion.” Although the amount of shape change is typically quite small, in view of the pixel structures used in modern displays, the distortion resulting from cutting can be large enough to lead to substantial numbers of defective (rejected) displays. Accordingly, the distortion problem is of substantial concern to display manufacturers and specifications regarding allowable distortion as a result of cutting can be as low as 2 microns or less.
The present invention is directed to controlling distortion and, in particular, to methods for controlling distortion in sub-pieces cut from glass sheets produced by a drawing process, such as, a downdraw, fusion downdraw, updraw, float, or similar process.